In recent years, CAD/CAM systems have been widely used to design dental prostheses such as inlays and crowns by computers to fabricate them by machining with milling machines. Conventionally, because of the importance laid on the aesthetic properties, ceramic materials have been generally used as the materials for mill blanks, which are materials to be machined usable in the present systems. However, since dental prostheses fabricated from mill blanks made of ceramics are brittle materials having high hardness, there are some disadvantages such as damages to opposing teeth or tooth chips caused by impact upon machining, occlusion, etc.
In order to solve the above problems, recently, studies on mill blanks made of composite materials containing a polymer resin or an inorganic filler have been made. Since the mill blanks made of the composite material have appropriate hardness that does not damage opposing teeth, and excellent impact resistance, the mill blanks have been worked into dental prostheses and be begun using them in clinical practices.
For example, Patent Publication 1 describes a mill blank for fabricating a dental prosthesis containing a polymer resin and an inorganic filler. As the fillers, a filler prepared by finely pulverizing a material obtained by sol-gel method, a commercially available irregular shaped barium glass filler, a filler prepared by pulverizing quartz with a mill, and an ultrafine particle inorganic filler (average particle size: 40 nm) have been studied.
In addition, Patent Publication 2 describes a mill blank for fabricating a dental prosthesis, containing an acrylic resin polymer and an ultrafine particle inorganic filler having an average particle size of from 0.01 to 0.04 μm.
Patent Publication 3 describes a resin cured product for dental medical care, comprising inorganic particles (composite particles) having a coating phase constituted by an acrylic polymer containing fluorine, and an acrylic polymer.
Patent Publication 4 describes a dental mill blank comprising a cured product of a curable composition containing a polymerizable monomer and a spherical inorganic filler having an average primary particle size of 0.1 μm or more and less than 1 μm.
Patent Publication 5 describes a method for producing a block for dental prosthesis process, including the steps of preparing a template provided with an inner surface shape corresponding to an outer surface shape of the block, filling a composite resin material containing a resin and an inorganic filler dispersed therein, capable of forming the above block by a curing treatment, subjecting the above composite resin to a rotary stirring treatment, while housing the above composite resin in the above template, and polymerizing the above composite resin material after the stirring treatment to cure. More specifically, it is a method for producing a block for dental prosthesis process, including filling a composite resin material containing an inorganic filler to a template having a block shape, rotary-stirring the contents to allow degassing, and thereafter allowing the composite resin material to polymerize and cure.
Patent Publication 6 describes a composite material suitable for a dental mill blank having a cross-network structure of glass and an organic resin, obtained by immersing a monomer in a porous support obtained by fritting glass powder, and thereafter allowing the monomer to polymerize and cure.
Further, Non-Patent Publication 1 describes a composite material suitable in dental mill blank obtained by immersing a polymer resin, or immersing a monomer and thereafter allowing the monomer to polymerize and cure, in a porous bulk-shaped ceramic sintered body having a communicated structure, thereby providing a dental mill blank having a interpenetrating network structure of ceramics and organic resins.